The present invention is related to an image display apparatus for enlarging and projecting an image and picture on an image displaying element such as a liquid crystal projector, DLP projector, and a rear projection TV.
Referring to FIGS. 14 to 14, an explanation is made for a projector as one example of the image display apparatus such as a liquid crystal projector, DLP projector, and rear projector for enlarging and projecting still images and moving images from a personal computer, as well as video image or TV pictures from a video camera or video recorder.
FIG. 14 is a perspective view illustrating an arrangement of parts of a prior projector without a cabinet (but indicated by dotted lines). FIG. 15 is a top view illustrating the part arrangement within the projector of FIG. 14. FIG. 16 illustrates a structure of a lamp house fitted within the same projector. FIG. 17 is a circuit block diagram of the same projector.
The image display apparatus (projector) 1PA includes a cabinet 2, an image display 3, the lamp house 4, a projection lens 5, a power supply 6, an ignitor module 7, a lighting device 8, a signal processing unit 9, a plurality of forced-air cooling fans 10, and an input filter 11.
The cabinet 2 forms a case which covers the whole projector, and is provided with the signal processing unit 9 extending on back and top of the cabinet 2 except for the lamp house 4.
The image display apparatus 1PA is connected to an AC mains 26 through an AC input cable 16. The AC input cable 16 is connected to the power supply 6 through the input filter 11. The voltage of the AC mains is, for example, 100 to 240 AC Volts, which is converted at the power supply 6 into DC voltages, such as DC 370 V, DC 12 V, DC 5 V, DC 3.3 V.
Connected to the power supply 6 are the signal processing unit 9 and the lighting device 8. The image display 3 is connected to the signal processing unit 9. The image display 3 includes an image displaying element 3a formed as a liquid crystal display or DMD element, and an optical system composed of a condenser lens and a prism (not shown) for focus control of a light from the discharge lamp 13. The image displaying element 3a receives an image signal output from the signal processing unit 9 to give the resulting image which is projected by means of a light from the discharge lamp 13 of which focus is controlled by the above optical system.
The lighting device 8 is connected to the lamp house 4. In detail, the lamp house 4 includes a high intensity discharge lamp 13, a reflector 13, and a lamp socket 14b (see FIG. 16). The discharge lamp 13 such as a metal halide discharge lamp and super high pressure mercury discharge lamp (refer to Japanese Patent Publication Nos. 2-138561 and 6-52830 for example) is connected to the lighting device 8 through high voltage lead wires 12 and the lamp socket 14b. The lamp house 4, which is detachable to the projector so that the user or operator can replace the discharge lamp 13, is partly or entirely made of a resin. Numeral 42 in FIG. 16 indicates a fixture of the reflector 30.
The projection lens 5 receives the light from the discharge lamp 13 through the image display 3 in order to enlarge and project the image or picture given to the image display 3.
The power supply 6 includes a rectifier 6a, a controller 6b, a boosting chopper circuit 6c, and four DC output circuits 6d to 6g. The rectifier 6a converts the input AC voltage into the DC voltage. The controller 6b controls the boosting chopper circuit 6c. The boosting chopper circuit 6c includes an inductance L1, a MOSFET (Q1), a diode D1, and a smoothing capacitor C1 to output a DC voltage boosted to a desired level by switching the MOSFET (Q1). The DC output circuits 6d to 6g are respectively DC-DC converters which convert the output of the boosting chopper circuit 6c into desired DC voltages for supplying the same to the corresponding units. The DC output circuits 6d to 6f supply appropriate DC voltages to the signal processing unit 9, while the DC output circuit 6g supplies an appropriate DC voltage to the lighting device 8.
The lighting device 8 includes a controller 8a, a step-down chopper 8b, a polarity inverting circuit 8c, resistors R2, R3 for lamp voltage detection, and a resistor R4 for lamp current detection. The controller 8a is supplied with a DC output from the DC output circuit 6g through a capacitor C7 so as to control the step-down chopper 8b and the polarity inverting circuit 8c based upon the lamp voltage and the lamp current respectively monitored by lamp voltage detection resistors R2, R3 and the lamp current detection resistor R4. The step-down chopper 8b includes a MOSFET (Q2), a diode D2, an inductance L3, and a capacitor C3 to step-down the input DC voltage supplied through a noise filter composed of an inductance L2 and a smoothing capacitor C2 for stably providing the electric power necessary to the discharge lamp 13 by switching the MOSFET (Q2). The polarity inverting circuit 8c, composed of MOSFETs (Q3 to Q6), inverts the polarity of the DC output of the step-down chopper 8c by switching MOSFETs (Q3, Q6) alternately with MOSFETs (Q4, Q5), thereby providing an AC power to the discharge lamp 13.
The ignitor module 7 includes a resistor R1, capacitors C4 to C6, a sidac SSS, transistors T1, T2, a diode D3, and a spark-gap (GAP). The ignitor module 7 derives its operating voltage from the output voltage of the step-down chopper circuit 8b within the lighting device 8 so as to apply high voltage pulses (for example, 18 kVo-p) between electrodes of the discharge lamp 13, bringing about a breakdown to thereby start lighting the lamp.
The signal processing unit 9 is connected at its input end to the personal computer, video recorder or the like through a signal cable 17, and at its output end to the image displaying element 3a of the image display 3. The signal processing unit 9 receives an RGB signal or TV signal from the computer, video recorders or the like connected to the signal cable 17, and outputs a signal for displaying the image on the image displaying element 3a. 
The forced-air cooling fans 10 are provided for avoiding a temperature rise of the heat-generating parts within the image display apparatus 1, and disposed respectively adjacent to the ignitor module 7, the power supply 6, and the lamp house 4.
The operation of the ignitor module 7 will be now explained in detail.
The ignitor module 7 operates on the output voltage from the step-down chopper circuit 8b, which charges capacitor C4 through resistor R1 so that sidac SSS become conductive to release the electric charges accumulated in capacitor C4 when capacitor C4 is charged to a break-over voltage of sidac SSS.
At this occurrence, a transient voltage is caused by a transient phenomenon in combination with an inductance as viewed from the primary side of the transformer T1, and is transferred to the secondary side of transformer T1, followed by being rectified to accumulate charge in capacitor C5. This action is repeated to increase the charged voltage across capacitor C5. When capacitor C5 is charged to the break-over voltage of the spark-gap (GAP), the spark-gap (GAP) conducts to discharge the capacitor C5. Upon this discharging, a voltage developed by a transient phenomenon in combination with an inductance as viewed from the primary side of transformer T2, is boosted at transformer T2 and is then output as high voltage pulses.
A recent technical problem for the projector concerns with a light-and-compact design for portability.
In making the projector compact, it is noted that the ignitor module 7 for igniting the light source of the discharge lamp 13 generates high voltage pulses which, as shown in FIG. 18, include frequency components of several MHz, and is cause to leak from the high voltage lead wires 12 by way of xe2x80x9cfloating capacitancexe2x80x9d present in various portions of the cabinet 2 while the pulses are fed through a transmission path (including the high voltage lead wires 12) from the ignitor module 7 as the high voltage pulse source to the discharge lamp 13. Thus leaked portion of the high voltage is voltage-divided by the floating capacitance to be dispersed to various portions of the cabinet 2.
Although the high voltage pulses are damped, they will be transmitted to microcomputer or IC in the signal processing unit 9 within the cabinet 2 due to this floating capacitance. When the high voltage pulses finally reaching the microcomputer or IC still have a voltage higher than a surge (or electrostatic) withstand at the corresponding terminals of the microcomputer or IC, the microcomputer or IC of the signal processing unit 9 will malfunction or even the signal processing unit 9 will be broken at the worst. In order to make a protection against this occurrence, the high voltage lead wires 12 should be made as short as possible and at the same time as thick as possible.
While, on the other hand, because of that the ignitor module 7 derives its operating voltage from the output voltage of the lighting device 8 and also because of that both of the ignitor module 7 and the lighting device 8 have their outputs connected to the discharge lamp 13, the ignitor module 7 and the lighting device 8 are formed commonly on a single board such that the ignitor module 7 and the lighting device 8 thus integrated together are disposed away from the signal processing unit 9 and close to the discharge lamp 13. Since the power supply 6 is disposed remote from the ignitor module 7 and the lighting device 8 for the discharge lamp 13, the ignitor module 7 and the lighting device 8 are provided with the noise filter 15 composed of inductance L1 and capacitor C2 in order to receive the electric power from the power supply 6.
Since the lighting device 8 is made active to keep the discharge lamp 13 turned on and is disposed adjacent to the discharge lamp 13, it is subject to a heat radiation from the discharge lamp 13 such that the electronic parts of the lighting device 8 suffer from increased temperature rise also in combination with heat resulting from a power loss of the lighting device 8 itself. In order to avoid this occurrence, it is necessary to provide the forced-air cooling fan 10 for the lighting device 8 or to design the path of the forced-air cooling flow within the cabinet 2.
Taken the above points into consideration, the projector of FIGS. 14 to 17 is designed.
Japanese Patent Publication No. 7-114805 discloses a lighting apparatus for vehicle""s head lamp, which is different from the image display apparatus of the present invention. The lighting apparatus includes a lamp body integrating a reflector, a discharge lamp integrated within the lamp body together with the reflector, a ballast for stably lighting the discharge lamp, and an ignitor applying a high starting voltage to the discharge lamp at the starring thereof. The ignitor has a high voltage generating unit which receives a low voltage input to generate a high voltage, and which is formed integrally with a connecting unit for the discharge lamp. The ballast and the ignitor is connected to the lamp body in such a manner that at least the connecting unit of the high voltage generating unit of the ignitor is exposed to the interior of the lamp body. In this lighting apparatus for the vehicle""s headlamp, a mounting unit for mounting the discharge lamp is not formed as integral part of the high voltage generating unit.
U.S. Pat. No. 3,180,981 proposes a technique in which a lighting device for an air-cooled projection lamp has high frequency terminals and is accommodated within a lamp house provided with an exhaust port in its top. The lighting device has its output connected to the lamp through high voltage lead wires and not at the high frequency terminals. An intake port for the lamp cooling air flow and the exhaust port are not limited to particular surfaces of the lamp house. Also, the interior of the image display apparatus and the lamp house are configured such that the air-cooling flow path is established when a cabinet of the image display apparatus is fitted with the lamp house.
U.S. Pat. No. 4,902,943 discloses a plug-in starting aid apparatus which is connected to a ballast as a starting circuit of a high intensity discharge lamp for providing high voltage pulses. In this apparatus, at least three terminals project from one face of a frame, the first one being connected a voltage-responsive switch, the second one being connected to a capacitor, and the third one connected to the end of a discharging loop. In this connection, the present invention as described later is not limited to the disclosed feature that the I/O terminals project out of a casing as well as that the individual terminals are provided for connection to the voltage-responsive switch, the capacitor and the end of the discharging loop, respectively.
However, the prior art structure has technical problems that the additional parts (noise filter 15, forced-air cooling fans 10 and the like) around the lighting device are required and that the signal processing unit 9 suffers from a malfunction due to that fact that the signal processing unit 9 are arranged within a narrow space together with the ignitor module 7 generating the high voltage pulses as well as the high voltage lead wires. Accordingly, it has been desired to restrain the malfunction of the signal processing unit 9, and more preferably, to prohibit the failure, to make the apparatus compact, to reduce the operational noise, to delimit the influence of the noise to the electronic circuitry, and to increase design flexibility.
The present invention has been accomplished in view of the above problems and has an object of providing an image display apparatus which is capable of restraining the malfunction of the signal processing unit.
The image display apparatus according to the present invention includes a cabinet which accommodates therein a discharge lamp, an ignitor module which applies a high voltage to the discharge lamp for igniting the same, a lighting device which is connected to the ignitor module and applies a discharging voltage to the discharge lamp so as to keep the discharge lamp turned on, a signal processing unit providing an image signal in accordance with an input signal, an image display which, in response to the image signal from the signal processing unit, produces an image to be projected by use of a light of the discharge lamp, and a power supply supplying an electric power to the ignitor module, the lighting device, the signal processing unit, and the image display. In this arrangement, at least a high voltage generating portion of the ignitor module is arranged to be separated from the lighting device and is disposed away from the signal processing unit and close to the discharge lamp, thereby restraining the malfunction of the signal processing unit. Also, since the high voltage generating portion of the ignitor module can itself form a single block so as to be freely arranged, in contrast to the prior art ignitor module which is incorporated into the lighting device, it can be arranged closed to the discharge lamp to reduce the leakage of the high voltage being applied to the discharge lamp, thereby enabling to reduce the malfunction or failure of the signal processing unit composed of electronic components such as a microcomputer and IC. Further, since the lighting device is away from at least the high voltage generating portion of the ignitor module, it can be arranged in a position not exposed to heat from the discharge lamp, whereby it is possible to reduce heat stress applied to the lighting device, and even to reduce the number of the forced-air cooling fans by suitably arranging the lighting device.
The ignitor module is preferred to have a lamp socket for restraining the high voltage pulsed from leaking to other portions by way of floating capacitance, thereby further restraining the malfunction or failure of the electronic circuitry of the microcomputer or IC.
Further, when the lighting device and the power supply are mounted on a common board, it is possible to eliminate the noise filter for suppression of high frequency noise superimposed on a connection line between the lighting device and the power supply and also to eliminate connectors for connection therebetween.
When the ignitor module is connected to the lighting device by wires, it is also possible to restrain the malfunction of the signal processing unit.
When the ignitor module and the lighting device are mounted on a flexible printed board, it is possible to eliminate the wires and to give an arrangement in which the ignitor module can be physically separated from the lighting device.
When the signal processing unit, the power supply, and the lighting device are mounted on opposite side of the ignitor module from the discharge lamp, it is possible to restrain the high voltage pulses from leaking to the other portions by way of the floating capacitances for restraining the malfunction or failure of the electronic circuitry of the microcomputer or IC.
Preferably, the ignitor module is composed of a high voltage generating circuit which applies the high voltage to the discharge lamp, and a power source circuit which is connected to the lighting device and provides an electric power to the high voltage generating circuit. Also, a lamp house is provided to be the cabinet and to have its interior space separated by a partition into two storage spaces, one for receiving the discharge lamp, and the other for receiving the high voltage generating circuit. Thus, the partition separating the two storage spaces can interrupt the heat radiation and ultraviolet radiation of the discharge lamp from reaching directly to the high voltage generating circuit of the ignitor module, avoiding the deterioration of the high voltage generating circuit of the ignitor module as well as the lowering of long-term reliability. As the lamp house is detachable to the cabinet, the high voltage generating circuit can be replaced with a new one simultaneously at the time of replacing the discharge lamp reaching its lamp life end, thereby realizing to provide a projector which is highly reliable in the ignition performance over a long-term use.
The high voltage generating circuit is surrounded by a case having walls, at least one of the walls forming an outer wall of the lamp house. With this arrangement, the case can interrupt the heat radiation and ultraviolet radiation of the discharge lamp from reaching directly to the high voltage generating circuit of the ignitor module, avoiding the deterioration of the high voltage generating circuit of the ignitor module as well as the lowering of long-term reliability.
The above partition is preferred to interrupt the heat radiation from the discharge lamp to the high voltage generating circuit.
Within the lamp house, there are provided lead wires for connection of the high voltage generating circuit to the power circuit of the ignitor module, and for connection of the discharge lamp to the lighting device, respectively. Preferably, the lamp house is provided with a partition which is disposed between the lead wires and the discharge lamp. Whereby, the partition can interrupt the heat radiation and ultraviolet radiation of the discharge lamp from reaching directly to the lead wires, avoiding the deterioration of the lead wires as well as the lowering of long-term reliability.
Preferably, the cabinet includes a fan which makes a forced-air cooling for the interior of the cabinet, and the high voltage generating circuit is arranged upstream of the discharge lamp with respect to a forced-air flow of the fan. With this result, the high voltage generating circuit of the ignitor module can efficiently radiate the heat.
Preferably, the high voltage generating circuit is connected to the discharge lamp through high voltage lead wires which extend from the high voltage generating circuit on its side adjacent to the discharge lamp. Thus, at the time of igniting the discharge lamp, it is possible to restrain the high voltage pulse generated at the high voltage generating circuit of the ignitor module from leaking through the floating capacitances present around various portions of the cabinet, reducing the danger of malfunctioning or breaking the microcomputer or IC.
The ignitor module is preferred to be separated into a high voltage generating unit for applying the high voltage to the discharge lamp and a power source unit which supplies an electric power to the high voltage generating unit. Thus, it is possible to restrain the malfunction or failure of the signal processing unit, to make the apparatus compact and light-weight, to reduce the operational noise, to delimit the influence of the noise to the electronic circuitry, to increase design flexibility, and yet to improve reliability of the apparatus even when the lamp house could not afford the space for accommodating the entire ignitor module.
The high voltage generating unit may be arranged close to the discharge lamp, enabling to improve reliability of the apparatus even when the lamp house could not afford the space for accommodating the entire ignitor module.
Preferably, the high voltage generating unit is arranged closer to the discharge lamp than the power source unit, thereby enabling to restrain the malfunction or failure of the signal processing unit, to make the apparatus compact and light-weight, to reduce the operational noise, to delimit the influence of the noise to the electronic circuitry, to increase design flexibility.
At least the high voltage generating unit is preferred to be arranged in the lamp house detachably receiving the discharge lamp. Thus, it is easy to modify the design of the high voltage generating unit of the ignitor module.
The lamp house is preferred to include a storage section receiving at least the high voltage generating unit for effectively avoiding the malfunction of the signal processing unit.
Preferably, the storage section is filled with an insulation material to enhance the insulation of the high voltage generating unit.